Iodide Sorption Research Articles

Retention of Iodide by Chloride Green Rust and Magnetite.

Green rust (GR), a layered double hydroxide (LDH) containing Fe, and magnetite can be found in natural and engineered environments. The ability of chloride GR (GR-Cl) and magnetite to retain iodide as a function of various parameters was investigated. Sorption equilibrium is achieved within 1 day of contact time between iodide and preformed GR-Cl in suspension. pHm variations (7.5-8.5) have no significant influence, but the iodide sorption decreases with increasing ionic strength set by NaCl. Sorption isotherms of iodide suggest that the uptake operates via ionic exchange (IC), which is supported by geochemical modeling. The short-range binding environment of iodide associated with GR is comparable to that of hydrated aqueous iodide ions in solution and is not affected by pHm or ionic strength. This finding hints at an electrostatic interaction with the Fe octahedral sheet, consistent with weak binding of charge balancing anions within an LDH interlayer. The presence of sulfate anions in significant amounts inhibits the iodide uptake due to recrystallization to a different crystal structure. Finally, the transformation of iodide-bearing GR-Cl into magnetite and ferrous hydroxide resulted in a quantitative release of iodide into the aqueous phase, suggesting that neither transformation product has an affinity for this anionic species.

Iodine Removal from Carbonate-Containing Alkaline Liquids Using Strong Base Resins, Hybrid Resins, and Silver Precipitation

The ability of several material types to remove aqueous iodine from a mildly alkaline, carbonate-rich nuclear waste stream was evaluated: strong base anion exchange resins (SBARs), hybrid resins, Ag-containing materials, and Bi-containing hybrid resins. A combination of batch testing and flow-through column testing was used in the evaluation. In batch testing, hybrid resins CHM-20, SIR-110-CE, and RTBI were shown to have high efficiency for the removal of both iodide and iodate simultaneously, while Ag-containing materials and SBAR demonstrated high capacity for iodide removal. One example of each material type (CHM-20, A532E, and Ionex 400) was further evaluated for their sorption isotherms and column performance. The Langmuir isotherm, or a Langmuir–Freundlich hybrid isotherm, best described the sorption of iodide to the CHM-20 hybrid resin and Purolite A532E. The Freundlich isotherm best described the uptake of iodate to CHM-20 and A532E and for both iodide and iodate to Ag-containing Ionex 400. In column testing, Purolite A532E had exceptional performance for overall iodide removal. However, with the capacity demonstrated, the A532E resin would exceed class C waste classification before breakthrough initiated, and column change-outs in processing would be dictated by eventual waste classification, not breakthrough. Ionex 400, a Ag-zeolite, was observed to degrade over time under mild alkaline column conditions, whereas the hybrid CHM-20 was limited in the single pass through design and would be best suited for applications where iodide and iodate are present and recirculation of the column effluent is feasible. This work highlights the feasibility of commercially available materials to separate radioiodine from liquid environments.

Critical Parameters and Mechanisms of Chromium Removal from Water by Copper-Based Nanoparticles

This research aims to explore the chromium removal from water using copper-based nanoparticles. The nanoparticles were synthesized by hydrothermal method and characterized by X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy as well as determination of the specific surface area (SBET) and point of zero charge (PZC). The size and composition of nanoparticles are influenced by the reaction time, organic coating, and oxidizing atmosphere. Sorption experiments were carried out in aqueous solutions as well as simulated drinking water at various initial concentration, time, and temperature. Cu nanoparticles had a significant Cr uptake capacity of 3.4 mg·g−1 for Cin 1.0 mg·L−1 lowering the Cr concentration below the provisional guideline value of 50 μg·L−1. Sorption isotherms were fitted to Henry, Langmuir, and Freundlich models, whereas kinetic data were reproduced by different kinetic models. Iodide sorption experiments were carried out to explore the sorption mechanism onto Cu-NPs. Considering the biocompatibility, stability, good uptake capacity, and reusability, Cu nanoparticles could be considered as promising agents for applications in water purification.

Adsorption of Aqueous Iodide on Hexadecyl Pyridinium-Modified Bentonite Investigated Using an Iodine–Starch Complex

The sorption affinity of iodide on organo-bentonite, modified with hexadecyl pyridinium (HDPy), was investigated with the iodine–starch method coupled with UV/Vis absorption spectroscopy. The iodine–starch complex method was optimized in terms of the reaction time and sample compositions, based on the UV/Vis absorbance. The batch sorption experiment for iodide on organo-bentonites, modified using two different loading amounts of HDPy, was conducted to analyze the influence of equilibrium time, liquid-to-solid ratio, and temperature, on the iodide sorption affinity. The experimental results regarding the removal capacity were further employed to derive the distribution coefficients of iodide on the organo-bentonites. The novelty of this work lies in the first application of the iodine–starch method coupled with UV/Vis absorption spectroscopy for analyzing the sorption behavior of iodide on modified bentonites. It is expected that the iodide-starch method can be complementarily employed for future research, with respect to the quantification of iodide.

Mechanisms and thermodynamic modelling of iodide sorption on AFm phases

Both, experimental and modelling evidence is presented in this study showing that interlayer anion exchange is the dominant sorption mechanism for iodide (I-) on AFm phases. AFm phases are Ca-Al(Fe) based layered double hydroxides (LDH) known for their large potential for the immobilization of anionic radionuclides, such as dose-relevant iodine-129, emanating from low- and intermediate-level radioactive waste (L/ILW) repositories. Monosulfate, sulfide-AFm, hemicarbonate and monocarbonate are safety-relevant AFm phases, expected to be present in the cementitious near-field of such repositories. Their ability to bind I- was investigated in a series of sorption and co-precipitation experiments. The sorption of I- on different AFm phases was found to depend on the type of the interlayer anion. Sorption Rd values are very similar for monosulfate, sulfide-AFm and hemicarbonate. A slightly higher uptake occurs by AFm phases with a singly charged anion in the interlayer (HS-AFm) as compared to AFm with divalent ions (monosulfate), whereas uptake by hemicarbonate is intermediate. No significant sorption occurs onto monocarbonate. Our derived thermodynamic solid solution models reproduce the experimentally obtained sorption isotherms on HS-AFm, hemicarbonate and monosulfate, indicating that anion exchange in the interlayer is the dominant mechanism and that the contribution of I- electrostatic surface sorption to the overall uptake is negligible.

Effect of Soil Organic Matter and Humates on Adsorption and Desorption Chemistry of Iodide in an Aridisol

The translocation of iodine (I) from soil to food chain is largely determined by its adsorption/desorption reaction in soils. In this study, the effects of commercial humates (HA) applied on an Aridisol and indigenous soil organic matter (SOM) on the adsorption and desorption of iodide were investigated. For this reason, 1% and 3% HA (w/w) were incorporated into the whole soil (WS) and organic matter free (OMF) soil samples. Then soil samples were equilibrated with 0, 2, 4, 6, 8 and 10 mg L-1 iodide solution prepared in 0.01 molar CaCl2 for 40 h. The sorption data were better described by Langmuir isotherm (R2= 0.938) than Freundlich isotherm (R2= 0.763). The Langmuir sorption maximum of WS was 19.8 mg kg-1. Freundlich isotherm parameters were n= 0.89 and Kf= 2.165. Sorption maximum of OMF soil significantly increased up to 35.5 mg kg-1. HA applications reduced iodide sorption maximum of both WS and organic OMF soil samples. Desorption rate of the WS ranged between 0-15.3% whereas it decreased 0-0.65% upon removal OM. HA treatments, in general, reduced the desorption rates. However, increasing HA application resulted in higher desorption ratio in both WS and OMF soils. Consequently, either SOM or HA has preeminent role in the adsorption-desorption chemistry in soils.

Use of silver\u2013bentonite in sorption of chloride and iodide ions

Ag–bentonite was prepared by ion exchange process to sorb iodide and chloride ions in batch experiments. The modified bentonite was examined with XRF and XRD. 75% of the cation exchange capacity was exchanged by silver ions. It was found that the sorption of chloride ions is an exothermic precipitation process because the solubility decreases with increasing temperature. In the case of iodide sorption, the dissolution of AgI was observed under high concentration of non-radioactive iodide ions, which is well known in analytical chemistry. The phenomenon occurs not only in the bulk aqueous phase but also in the interlayer space of montmorillonite.

Sorption characteristics of iodide on chalcocite and mackinawite under pH variations in alkaline conditions

Abstract In terms of long-term safety for radioactive waste disposal, the anionic iodide (I-129) with a long half-life (1.6 × 106 yr) is of a critical importance because this radionuclide migrates in geological media with limited interactions. Various studies have been performed to retard the iodide migration. Recently, some minerals that are likely generated from waste container corrosion, have been suggested to have a considerable chemical interaction with iodide. In this study, chalcocite and mackinawite were selected as candidate minerals for underground corrosion materials, and an iodide sorption experiment were carried out. The experiment was performed under anoxic and alkaline conditions and the pH effects on the iodide sorption were investigated in the range of pH 8 to 12. The results showed that both minerals demonstrated a noticeable sorption capacity on iodide, and the distribution coefficient (Kd) decreased as the pH increased in the experimental condition. In addition, when the alkalinity increased higher than a pH of 12, the sorption capacity of both minerals decreased dramatically, likely due to the competition of hydroxy ions with the iodide. This result confirmed that chalcocite was an especially good sorbing media for iodide under alkaline conditions with a pH value of less than 12.

Influence of physicochemical properties of various soil types on iodide and iodate sorption

Studies that deal with iodine mobility in uncontaminated agricultural soils are scarce and unique. Therefore, in this article, we have evaluated the sorption behavior of two most abundant naturally occurring inorganic iodine species – iodide and iodate – in several soil types. Our results showed that the sorption process is extremely slow with equilibrium achieved after ten days. The sorption of both iodine species is well described by Freundlich isotherm. The affinity of iodine for all investigated soils in the observed concentration range is relatively low. Our results showed that besides iodine speciation, sorption efficiency is highly dependent on soil types and their characteristics. While in mineral soils with low organic carbon content iodide sorption is dominant, organic rich soils are more favorable for iodate sorption. Organic carbon, clay content, pH and the abundance of iron, aluminum and manganese oxides and hydroxides showed to be the most important soil properties controlling iodine sorption. Our results provide new insight into the complex iodine behavior and retention in soils. This is crucial for better understanding of iodine mobility and the ability to enter the food chain.

Dynamic sorption properties of Metal-Organic Frameworks for the capture of methyl iodide

In this work, methyl iodide (CH3I) sorption properties of Metal-Organic Frameworks (MOFs) were experimentally studied. CH3I adsorption capacities were determined at 35 °C for the different prototypical selected MOFs, MIL-53(Al), MIL-100(Al), MIL-120(Al), CAU-1(Al), UiO-66(Zr), HKUST-1(Cu) and ZIF-8(Zn) from fixed-bed reactor measurements by using infrared spectroscopy. Quantitative exploitation of breakthrough curves reveals higher sorption performances (Qsat up to 425 mg/g) for materials showing pore size and geometry well-adjusted to CH3I dimension, such as MIL-120(Al), MIL-53(Al) and HKUST-1(Cu). In situ DRIFTS (Diffuse Reflection Infrared Fourier Transform Spectroscopy) experiments were also carried out in order to further investigate the interaction modes of physisorbed CH3I species within MIL-53 and MIL-120 compounds. For MIL-120, the confinement of adsorbed CH3I molecules within the pores is strengthened by specific interactions with the ligand and hydroxyl groups. For a breathing compound like MIL-53(Al), the adsorption measurement confirmed a swelling related to CH3I adsorption.

Sorption of iodide (I−) from aqueous solution using Mg/Al layered double hydroxides

In this article, the authors report the adsorption of iodide by Mg/Al LDHs and thermally activated LDH materials in laboratory scale batch experiments. The optimal Mg/Al cation ratio was 3:1while the percentage iodide uptake increased with increasing adsorbent dose up to 1g/20mL of solution. The effect of initial iodide concentration was investigated using the Langmuir and Freundlich adsorption isotherm models, while the pseudo second order kinetic model appeared to provide the best fit for the experimental data. High iodide uptake of over 80% could be achieved without completely eliminating dissolved or atmospheric carbonate and leaching of 131I from LDHs did not appear to be a significant problem over the period of 28days investigated. These results demonstrate that LDHs, which are already commercially available in large quantities, are a technology that shows considerable promise for the removal of radioiodine from aqueous solution.

Iodide removal using LDH technology

The presence of radioactive iodine (radioiodine) in drinking water is a significant health hazard that originates from nuclear medicine and atomic energy industries. The application of LDHs to the removal of iodine offers potential for iodine capture and entrapment. Mg/Al and Zn/Al layered double hydroxides (LDHs) have been prepared and have been evaluated for the sorption of iodide in some small-scale batch experiments. All LDHs were prepared by the co-precipitation method and characterised by a range of techniques including powder X-ray diffraction, transmission electron microscopy and elemental analysis. Adsorption experiments were carried out at high iodide concentrations up to 1000ppm and no control or pH or atmospheric carbonate commonly used in most studies. The highest iodide uptake of approximately 71% was observed using a 3:1 Zn/Al LDH thermally activated to 500°C, however, a 3:1Mg/Al LDH exhibited similar results. LDHs potentially offer a technology for the removal of iodine from aqueous media.

Uptake of radioiodide by Paenibacillus sp., Pseudomonas sp., Burkholderia sp. and Rhodococcus sp. isolated from a boreal nutrient-poor bog

Radionuclides, like radioiodine (129I), may escape deep geological nuclear waste repositories and migrate to the surface ecosystems. In surface ecosystems, microorganisms can affect their movement. Iodide uptake of six bacterial strains belonging to the genera Paenibacillus, Pseudomonas, Burkholderia and Rhodococcus isolated from an acidic boreal nutrient-poor bog was tested. The tests were run in four different growth media at three temperatures. All bacterial strains removed iodide from the solution with the highest efficiency shown by one of the Paenibacillus strains with >99% of iodide removed from the solution in one of the used growth media. Pseudomonas, Rhodococcus and one of the two Paenibacillus strains showed highest iodide uptake in 1% yeast extract with maximum values for the distribution coefficient (Kd) ranging from 90 to 270L/kg DW. The Burkholderia strain showed highest uptake in 1% Tryptone (maximum Kd 170L/kg DW). The Paenibacillus strain V0-1-LW showed exceptionally high uptake in 0.5% peptone +0.25% yeast extract broth (maximum Kd>1,000,000L/kg DW). Addition of 0.1% glucose to the 0.5% peptone +0.25% yeast extract broth reduced iodide uptake at 4°C and 20°C and enhanced iodide uptake at 37°C compared to the uptake without glucose. This indicates that the uptake of glucose and iodide may be competing processes in these bacteria. We estimated that in in situ conditions of the bog, the bacterial uptake of iodide accounts for approximately 0.1%–0.3% of the total sorption of iodide in the surface, subsurface peat, gyttja and clay layers.

Selective sorption of iodide onto organo-MnO2 film and its electrochemical desorption and detection

This paper reports an electrochemically grown film consisting of layered MnO2 intercalated with hexadecylpyridinium cations (HDPy+), which can selectively sorb and detect iodide anions in aqueous solution amperometrically. Sorption of iodide by the HDPy/MnO2 film did not occur via ion exchange, but through hydrophobic interactions between the interlayer organic phase of the film and iodide ions in solution. The sorption rate increased with the deposited amount of MnO2. During the sorption process, the interlayer spaces expanded, and new diffraction peaks appeared that were attributed to the incorporated species. Anodic polarization of the iodide-sorbed HDPy/MnO2 film led to electron transfer from the incorporated iodide to the underlying substrate through the MnO2 sheets. The oxidized iodide was expelled from the film as molecular I2, while the expanded interlayer spaces were restored to their original state. Thus, the MnO2 layers and the incorporated HDPy can synergistically sorb/desorb iodide anions, resulting in a unique “self-cleaning” function that can operate electrochemically. This property allowed amperometric detection of iodide at a concentration as low as 0.0186μM, which was below the detection limits reported for previous iodide sensors.

Sorption of radioiodide in an acidic, nutrient-poor boreal bog: insights into the microbial impact

Batch sorption experiments were conducted to evaluate the sorption behaviour of iodide and the microbial impact on iodide sorption in the surface moss, subsurface peat, gyttja, and clay layers of a nutrient-poor boreal bog. The batch distribution coefficient (Kd) values of iodide decreased as a function of sampling depth. The highest Kd values, 4800 L/Kg dry weight (DW) (geometric mean), were observed in the fresh surface moss and the lowest in the bottom clay (geometric mean 90 mL/g DW). In the surface moss, peat and gyttja layers, which have a high organic matter content (on average 97%), maximum sorption was observed at a pH between ∼4 and 5 and in the clay layer at pH 2. The Kd values were significantly lower in sterilized samples, being 20-fold lower than the values found for the unsterilized samples. In addition, the recolonization of sterilized samples with a microbial population from the fresh samples restored the sorption capacity of surface moss, peat and gyttja samples, indicating that the decrease in the sorption was due to the destruction of microbes and supporting the hypothesis that microbes are necessary for the incorporation of iodide into the organic matter. Anoxic conditions reduced the sorption of iodide in fresh, untreated samples, similarly to the effect of sterilization, which supports the hypothesis that iodide is oxidized into I2/HIO before incorporation into the organic matter. Furthermore, the Kd values positively correlated with peroxidase activity in surface moss, subsurface peat and gyttja layers at +20 °C, and with the bacterial cell counts obtained from plate count agar at +4 °C. Our results demonstrate the importance of viable microbes for the sorption of iodide in the bog environment, having a high organic matter content and a low pH.

Preparation, characterization, and iodide sorption performance of silver-loaded mesoporous MCM-41

Mesoporous MCM-41 has been modified by incipient wetness impregnation with silver atoms as a new sorbent for iodide. The Ag-modified mesoporous MCM-41 (Ag-MCM-41) was characterized using X-ray diffraction, surface area, pore volume and pore size analyzer, and scanning electron microscopy/energy dispersive spectroscopy techniques, and its sorption behavior for iodide was studied. The effects of pH, contact time, temperature, initial concentration of iodide, and competing anions such as chloride and fluoride were investigated by batch method. The sorption capacity was very high in the pH range of 1.0–3.0. The kinetic analysis revealed that the overall sorption process was fitted with the pseudo-second-order kinetic model. The experimental sorption isotherm is also successfully described by Langmuir and Freundlich models. The maximum sorption capacity of iodide onto Ag-MCM-41 was found to be 238.1 mg g−1.

Effects of radiation and temperature on iodide sorption by surfactant-modified bentonite.

Bentonite, which is used as an engineered barrier in geological repositories, is ineffective for sorbing anionic radionuclides because of its negatively charged surface. This study modified raw bentonite using a cationic surfactant (i.e., hexadecyltrimethylammonium [HDTMA]-Br) to improve its sorption capability for radioactive iodide. The effects of temperature and radiation on the iodide sorption of surfactant-modified bentonite (SMB) were also evaluated under alkaline pH condition similar to that found in repository environments. Different amounts of surfactant, equivalent to the 50, 100, and 200% cation-exchange capacity of the bentonite, were used to produce the HDTMA-SMB for iodide sorption. The sorption reaction of the SMB with iodide reached equilibrium rapidly within 10 min regardless of temperature and radiation conditions. The rate of iodide sorption increased as the amount of the added surfactant was increased and nonlinear sorption behavior was exhibited. However, high temperature and γ-irradiation ((60)Co) resulted in significantly (∼2-10 times) lower iodide Kd values for the SMB. The results of FTIR, NMR, and XANES spectroscopy analysis suggested that the decrease in iodide sorption may be caused by weakened physical electrostatic force between the HDTMA and iodide, and by the surfactant becoming detached from the SMB during the heating and irradiation processes.

Effective and Selective Sorption of Iodide by Thin Film of Multilayered MnO2 Intercalated with Cationic Surfactants

We have fabricated a thin film of multilayered MnO2 whose interlayer is occupied with hexadecylpyridinium (HDPy) cations, using a simple anodic approach. The resulting film can effectively sorb iodide anions from aqueous solutions, even in the presence of NaCl or Na2SO4. The maximum sorption capacity was estimated to be 256 mg/g-MnO2, whereas a layered MnO2 film intercalated with K(+) ions showed no significant sorption. The layered structure of the HDPy/MnO2 composite remained unchanged after a sorption experiment. This indicates the incorporation of I(-) ions between MnO2 layers due to their specific affinity toward HDPy.

Mineral Synthesis in Si–Al–Ca Systems and Their Iodide Sorption Capacity under Alkaline Conditions

The release of anionic nuclides such as 129I from underground nuclear waste disposals is of great environmental concern due to its long half-life and high mobility in alkaline environments. The leachability of iodide is largely dependent on the sorption capacity of various Ca-bearing minerals such as ettringite, hydrocalumite, and calcium silicate hydrate (C-S-H) which are common hydration products of cement materials. Moreover, the pore water chemistry of cement materials is dominated by Si, Al, and Ca during the initial stage of weathering, and the ratios of the ions present vary much depending on the source materials. Examining the mineral phases generated in Si–Al–Ca systems with respect to different ratios of Si, Al, and Ca and their interaction with iodide is important to better understand the sorption behavior of iodide in nuclear waste disposal facilities. In this study, the mineral synthesis in Si–Al–Ca systems was conducted under alkaline conditions at ambient temperature, and the sorption behavior of iodide with the mineral phases was investigated during and after the mineral formation. The results showed that portlandite, C-S-H, stratlingite (CASH), hydrocalumite, gibbsite, and amorphous compounds were precipitated from the systems, depending on the Si, Al, and Ca ratios. The Kd values of iodide were greatly affected by the Ca content and relatively high Ca-containing phases such as hydrocalumite, C-S-H, CASH, and portlandite showed high iodide retention capacity. Hence, ensuring the formation of these secondary minerals by modification of the chemical composition of cement materials could assist in safety design of nuclear waste disposals.

Laccase-Catalyzed Oxidation of Iodide and Formation of Organically Bound Iodine in Soils

Laccase oxidizes iodide to molecular iodine or hypoiodous acid, both of which are easily incorporated into natural soil organic matter. In this study, iodide sorption and laccase activity in 2 types of Japanese soil were determined under various experimental conditions to evaluate possible involvement of this enzyme in the sorption of iodide. Batch sorption experiment using radioactive iodide tracer ((125)I(-)) revealed that the sorption was significantly inhibited by autoclaving (121 °C, 40 min), heat treatment (80 and 100 °C, 10 min), γ-irradiation (30 kGy), N(2) gas flushing, and addition of reducing agents and general laccase inhibitors (KCN and NaN(3)). Interestingly, very similar tendency of inhibition was observed in soil laccase activity, which was determined using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as a substrate. The partition coefficient (K(d): mL g(-1)) for iodide and specific activity of laccase in soils (Unit g(-1)) showed significant positive correlation in both soil samples. Addition of a bacterial laccase with an iodide-oxidizing activity to the soils strongly enhanced the sorption of iodide. Furthermore, the enzyme addition partially restored iodide sorption capacity of the autoclaved soil samples. These results suggest that microbial laccase is involved in iodide sorption on soils through the oxidation of iodide.